The present invention relates to an apparatus for feeding a high-pressure fluid, in which fuel is injected, in response to the fuel injection timing, into each cylinder of a diesel engine, from a fuel injection valve attached to the cylinder, and more specifically to a fuel injection apparatus using piezoelectric elements for fuel injection control.
As an example of conventional apparatuses for feeding a high-pressure fluid, there is a system which feeds and injects fuel into, e.g., each cylinder of a diesel engine. In this fuel injection system, the fuel discharged from a fuel injection pump, which is driven by the engine, is fed to a fuel injection valve in response to the injection timing. The fuel delivery, injection timing, etc., are adjusted to optimum conditions for the operating state of the engine. The establishment of these conditions requires sophisticated adjusting mechanisms, such as a governor and timer mechanism.
As a means of settling this problem, for example, an actuator mechanism using piezoelectric elements is disclosed in Japanese Patent Disclosure No. 183069/84. This mechanism, which serves for combined use with fuel injection valve and fuel injection pump, controls the voltage applied to the piezoelectric elements, thereby extending or contracting the elements. Thus, the fuel injection timing, as well as injection quantity, can be determined properly.
The piezoelectric elements constituting the actuator mechanism are extended when supplied with high voltage. Therefore, they can effectively be utilized for the execution of a delicate, high-speed action, in particular.
When using these piezoelectric elements for the arrangement of, for example, a pump, high voltage is applied to the elements to extend them for pump discharge. Thus, although the pump including the piezoelectric elements has a high-speed response characteristic, its actual discharge efficiency depends on the instantaneous current supply capability of its drive power source. In other words, the operating characteristic of the pump using the piezoelectric elements is determined by the capacity of a power circuit of the elements. If a fuel injection apparatus is constructed by the use of the piezoelectric elements, for example, a large-scale, high-voltage power source unit is required, which can instantaneously supply a large current to the piezoelectric elements which serve as a source of injection power for the apparatus.
The extension of the piezoelectric elements supplied with the high voltage is influenced by temperature, frequency of applied voltage, and the like. When using these elements in the fuel injection apparatus, therefore, it is difficult to maintain steady injection characteristics.